Design

In the fall of 1941 Cadillac suggested to the Ordnance Department that they should try the M3 with a twin Cadillac engine due to radial engine shortages that were used by the aircraft industry. It was also to have the Cadillac Hydra-matic transmission that was used in automobiles.

In February 1942 an M3A1 had 2 Cadillac liquid cooled V-8 car engines installed which meant that the rear deck had to be raised. Fuel tanks were put in the rear corners of the hull. Radiators were placed above the engines.

The flywheel in each engine was connected to the Hydra-Matic Transmission. Since the drive shaft from the Cadillac engines and the Hydra-Matic transmission, some of the traversing mechanisms and parts of the gun stabilizer were moved under the turret basket and this provided more room for the commander and gunner. The turret was extended in back to accommodate the radio.

A single cylinder engine supplied auxiliary power and charged the batteries.

Crew

The seats for the driver and assistant driver could be locked in any position. The seats went up under spring pressure and down under body weight. The driver and assistant driver had 360° periscopes in the roof of the hull.

Four escape hatches were provided.

New Designation

It was originally going to be designated the M4 Light Tank, but it was decided to use M5 to avoid confusion with the M4 Medium.

Armor

The M5's hull was welded armor plating with the front plate reinforced. The turret was also welded.

Armament

The M5's 37 mm M6 gun could fire an APC shell at a muzzle velocity of 2,900'/sec. It's range was 12,850 yards. At 1,000 yards the M6 gun could penetrate 1.8" of armor.

There was a gyrostabilizer which helped keep the gun at a fixed elevation during movement.

Prototype

The Ordnance Board was convinced that a car engine would work, so Cadillac converted a tank and drove it for 500 miles at a testing ground. The test showed it to have a smooth ride and was easy to operate. The Ordnance Board was convinced and production commenced.

Production

Standardized in February 1942. Production started in July 1942.
First production units were delivered at the end of March 1942.

In July 1943, another Cadillac production facility in Southgate, California, and Massey-Harris in Racine, Wisconsin, also started production. When M3 production ceased in October 1943, American Car & Foundry started production of the M5.

T8E1 Reconnaissance Vehicle: Was fitted with racks to carry land mines.

T27, T27E1 81 mm Mortar Motor Carriage: The army wanted a mortar carrier based on the M5A1 chassis. The T27 prototype had the turret removed and an armored superstructure installed. The mortar was to fire forward with a 35 degree traverse. A .50 cal MG was also installed. The T27E1 had the mortar lower in the hull so that it didn't stick above the superstructure. Project canceled in April 1944 due to inadequate crew and storage space.

T29 4.2" Mortar Motor Carriage: After the T27 was canceled a design that had more space internally and used a smaller mortar was devised, however, this too had too small of space.

T82 Howitzer Motor Carriage: Had 75 mm howitzer in a mount in the front of the hull. It was intended for jungle warfare but the design was abandoned in May 1945.

British Use

Nicknamed "Honey" by British calvary regiments. 84 sent to 8th Army in July 1941. Used in Burma, New Guinea, Iraq, Britain, NW Europe, Italy, and North Africa. Russia, China, New Zealand, and France received some as well.

The British were reported to like this tank at the time of its introduction. It could go about 10-20 mph faster than their own or enemy tanks, and required less maintenance.